a) Field of the Invention
The present invention relates to an ion implantation system and method, and more particularly to an ion implantation system and method suitable for implantation by a low energy ion beam.
b) Description of the Related Art
High integration of CMOS semiconductor integrated circuit devices nowadays is associated with some problem of short channel effects which may cause a lowered performance of MOS transistors, a lowered drain current, a threshold value shift and the like. Shallow source and drain regions are effective for suppressing the short channel effects. In order to form shallow source and drain regions, it is desired to use a low energy ion beam for ion implantation.
When ions are implanted at a low energy, a process time per unit doping amount becomes long because the ion beam current is small. In order to avoid a prolonged process time, it is necessary to increase the ion beam current at a low energy. As the beam current is increased, the ion beam becomes likely to be diverged by the space-charge effects. In order to prevent ion beam divergence, a method has been proposed which converges an ion beam by disposing an electrostatic lens along a beam line.
The present inventors have found that ion implantation with a low energy ion beam converged by an electrostatic lens is not, however, sufficient for forming shallow source and drain regions.